Electro-magnetic interference (EMI) is a kind of electrical pollution which has been recently discovered. Advances in technology have caused increased electro-magnetic radiation in populated environments. When the electro-magnetic radiation is not shielded effectively, it might interfere with daily communications and result in inaccurate analysis of various electronic instruments, or even endangering human health. Therefore, there is an increasing demand for a material with high electro-magnetic interference shielding ability.
Electro-magnetic radiation is mainly caused by an electrical field and a magnetic field perpendicular to each other. Therefore, the electro-magnetic interference shielding may be divided into electrostatic field shielding and magnetostatic field shielding. The electrostatic field shielding is performed by using electric charges on the surface of a metal to offset the electrical field inside the metal. On the other hand, the magnetostatic field shielding is performed by using a ferromagnetic material with high magnetic permeability to provide a low-resistant path, such that magnetic force line can be conducted through or reach the shielding material. In other words, the electro-magnetic interference shielding principles can work by reflection loss and absorption loss. A highly electrical conductive material has low volume resistance and thus has high reflection loss. A hysteresis loop of a magnetic material depends on its saturated magnetization and coercivity. The higher the saturated magnetization and coercivity are, the larger the encapsulation surface of the hysteresis loop is, resulting in higher energy loss and higher electro-magnetic interference shielding ability.
Metallic materials with high electrical conductivity are commonly used EMI materials. However, the metallic materials are usually heavy, highly corrodible, and have high hardness.
Although materials having both conductive and ferromagnetic properties have been developed, they are not satisfactory in all aspects. For example, nanocomposites do not possess sufficient conductive or ferromagnetic properties or are difficult to process due to poor dispersity.
Therefore, a novel EMI material with high conductive and ferromagnetic properties which is light, easy to process, flexible, or incorrodible is desired.